The Physics of Sailing

Effective Sailing is dependent on balancing 3 basic forces:

1. the driving force of the wind, caused by wind flowing across the sail

2. the sideways force

3. the heeling force

The Velocity of the wind relative to the boat results in a force that acts on the sails. This force has two components, one perpendicular and one parallel. "Lift" is the force component that acts perpendicular to the wind direction, while "Drag" acts parallel to the wind direction.

The sideways and heeling forces are a result of the force exerted by the water on the hull and the keel of the boat (a structure that provides support and resembles a wing of an airplane). This force of water also has both perpendicular and parallel components, and the keel offers a counter force to minimize the sideways movement of the boat.

Sailboat racers rely on physics principles to properly adjust their sail and boat angle to the wind to maximize their speed. The optimal wind angle for achieving good boat speed is when the wind blows directly over the side of the boat. At this angle, the lift force points in the forward direction, and the forward push force of the wind on the sails remains constant, and is independent of the speed of the boat. Therefore, a sailboat is able to reach speeds that are faster than the wind itself!

Here's an interesting video that gives some context into sail trim, and the speed that boats can achieve!

http://www.youtube.com/watch?v=FWINygISxDE